Monitoring and process control of the additive manufacture of a workpiece

ABSTRACT

In order to allow real-time monitoring of a tracing process during additive manufacture, a device is disclosed for the additive manufacture of a workpiece. A scanning unit (2) is designed to direct a fusing beam (3) onto a tracing spot (4). The device also has a local-resolution optical detector (5), a control unit (6) and an imaging unit (7). The imaging unit (7) is designed to image a portion (8) of the tracing surface (1) on the detector (5). The control unit (6) is designed to control the device in order to change the position of the portion (8) during manufacture.

The invention relates to a device for the additive manufacture of a workpiece, which has a scanning unit, which is designed to direct a fusing beam, also referred to as a tracing beam, onto a tracing point on a tracing surface, and also an optical detector, a control unit and an imaging unit. The invention also relates to a method for monitoring the additive manufacture of a workpiece, and to a method for the process control of the additive manufacture of a workpiece and to a corresponding computer program.

The document US 2016/0184893 A1 describes monitoring of additive manufacturing processes, in particular in the case of selective laser melting, by means of a pyrometer or a photodiode.

In the case of known methods for the monitoring of an additive manufacturing method, it is often difficult or impossible to detect defects or imperfections, which already impair the tracing process.

Against this background, the object of the present invention is to provide an improved concept for the additive manufacture of a workpiece that allows real-time monitoring of the tracing process in order to be able to detect defects or flaws already during the tracing process.

According to the invention, this object is achieved by a device, a method for monitoring and process control and a computer program according to the independent patent claims. Advantageous developments and embodiments are the subject of the dependent claims.

The improved concept is based on the idea of providing a spatially resolving detector for monitoring a tracing surface and of dynamically changing a position of a subregion of the tracing surface observed by means of the detector during manufacture.

According to a first independent aspect of the improved concept, a device for the additive manufacture of a workpiece is provided. The device has a scanning unit, which is designed to direct a fusing beam onto a tracing point on a tracing surface. The device also has an optical detector, a control unit and an imaging unit. The detector is formed as a spatially resolving detector and the imaging unit is designed and arranged to image a subregion of the tracing surface at least two-dimensionally by means of the detector. The control unit is designed to activate the device, in particular the imaging unit or the scanning unit, to change a position of the subregion during manufacture.

The fusing beam may be for example a light beam, in particular laser beam, an electron beam or some other energy beam that is suitable for additive manufacture, in particular for selective additive manufacture.

The tracing surface may be for example a surface or part of the surface of a powder bed from which the workpiece is manufactured. The tracing surface may include part of the powder bed surface and part of a workpiece surface. The tracing surface may be the workpiece surface or part of the workpiece surface, for example in the case of manufacturing methods without a powder bed, in which for example material is applied directly to the workpiece surface and is fused.

The additive manufacture may be an additive manufacturing method, in particular a selective additive manufacturing method, for example electron beam melting, selective laser melting (SLM) or selective laser sintering (SLS).

The detector may be for example a camera, a camera detector or camera sensor or a camera may include the detector.

That the detector is formed as a spatially resolving detector may mean that the detector has multiple pixels, in particular an array of pixels. For example, the detector may contain several 1000 pixels, in particular an array with a number of pixels in the range of 100 000 pixels to 10 000 000 pixels.

The use of such a spatially resolving detector allows the subregion to be imaged quickly, with high resolution and with high quality.

The imaging of the subregion on the detector takes place for example in the visible and/or infrared range. Correspondingly, the detector is sensitive in the visible and/or infrared range.

Here and hereinafter, the term “light” may be understood as comprising electromagnetic waves in the visible range, in the infrared range and/or in the ultraviolet range. Accordingly, the term “optical” may be understood as relating to light according to this understanding.

The scanning unit, which may also be referred to as the scan unit or deflecting unit, serves in particular for deflecting the fusing beam in a controlled way, and thereby controlling the tracing point on the tracing surface in order to carry out the selective manufacture of the workpiece according to a defined work order, in particular according to a defined work program.

The two-dimensional imaging of the subregion may be two-dimensional imaging. In particular, a surface of the subregion is not necessarily planar or flat, which may have the effect that in the subregion there are different heights, for example of the powder bed, that is to say there is a topography.

The at least two-dimensional imaging of the subregion may also be understood as two-and-a-half-dimensional imaging, in the sense that, apart from coordinates which lie in a base plane of the tracing surface or of the powder bed, associated items of topography information, that is to say height information, are recorded by the imaging onto the detector. In this case, the term “two-and-a-half-dimensional” may be understood such that the third dimension is available to the two-dimensional plane coordinates as an attribute or function. For each pair of Cartesian plane coordinates, in a two-and-a-half-dimensional model there exists precisely one height coordinate. Consequently, for example, vertical walls or overhangs or hollow spaces that would require complete 3D imaging cannot be recorded by means of a two-dimensional imaging.

The at least two-dimensional imaging of the subregion may also be a three-dimensional imaging.

According to at least one embodiment, the subregion does not cover the entire tracing surface or the entire powder bed. The subregion is therefore smaller than an entire working region. As a result, the achievable spatial resolution and the corresponding imaging quality and image quality are further increased.

The position of the subregion may be changed by being activated by the control unit, in that a deflection of imaging beams or imaging light for the imaging of the subregion is deflected by the scanning unit synchronously with the fusing beam. This is the case for example in embodiments in which the imaging beam or the imaging light is coupled into a beam path of the fusing beam.

As an alternative or in addition, the changing of the position of the subregion may take place by being activated by the imaging unit, in particular activated by the control unit, for example in embodiments in which the camera includes its own dynamic system for changing its image region.

According to various embodiments, the described steps of the method are repeated after changing the position of the subregion. This allows monitoring of the tracing surface, in particular a region around the tracing point, directly at the time of manufacture, that is to say in real time, also referred to as “online” monitoring.

According to various embodiments, the tracing point lies within the subregion, in particular the tracing point always lies in the subregion during the additive manufacture, which means that the subregion is changed in such a way that it follows a movement of the tracing point, or vice versa.

Due to the spatially resolved observation and imaging of the restricted subregion in comparison with the entire tracing surface, and due to the dynamic changing of the position of the subregion, qualitatively high-grade records of relevant regions on the tracing surface, in particular regions around the tracing point, are recorded in real time, or almost in real time, during manufacture and are made available. These records can be used for assessing or monitoring the manufacturing progress, the manufacturing quality or other manufacturing parameters, in particular visual and/or thermal assessment. The assessment may be performed for example by humans or in a computer-aided or fully automatic manner.

The use of an extended array of pixels makes quicker and more efficient imaging of relevant regions possible than would be the case for example with a point-like detector, which ultimately makes real-time observation, or almost real-time observation, possible in the first place.

The assessment of the additive manufacture may for example comprise the observing or identifying of defects or possible defects or of flaws, in particular directly before the tracing point. The assessing or observing may also include a detection of elevations, defects, spatter, debris and so forth on the tracing surface, while these may occur for example during the manufacturing process or a subsequent coating process. In particular, they may occur during an earlier tracing process of adjacent structures in the surrounding area of the current tracing point. According to the improved concept, it is possible to adequately address and respond to such disturbances and flaws.

In particular, by means of a device according to the improved concept, the assessment or observation of the manufacturing process can be used to the extent that elevations and other faults or imperfections are taken into account in a coating process following manufacture or included in manufacture.

According to at least one embodiment of the device, the scanning unit has a beam splitter, which is arranged on an input side of the scanning unit in a beam path of the fusing beam.

The scanning unit has in this case an input side and in particular an output side, wherein the input side is facing a source of the fusing beam, that is to say in particular a heating, tracing, radiating, electron or laser source, while the output side is facing the tracing surface or the powder bed and the workpiece. Such embodiments are suitable in particular for methods in which the fusing beam is a laser beam, for example for SLS or SLM methods.

The beam splitter is in particular arranged in such a way that imaging light that impinges on the beam splitter from the tracing surface via the deflecting unit is at least partially coupled out from the beam path of the fusing beam and directed in the direction of the detector.

The scanning unit advantageously acts in a way analogous to how it acts on the fusing beam also on the imaging light or the imaging beam. Accordingly, the observed subregion is always coupled to the fusing beam, in particular the tracing point.

In various embodiments, the tracing point is located in particular at a center, or almost at a center, of the subregion. On account of the synchronous deflection of the fusing beam and the imaging beam, the coupling of the subregion to the fusing beam and the tracing point is independent of a current direction or deflection of the fusing beam or a corresponding deflecting state of the scanning unit.

This has the advantage in particular that, during the changing of the subregion or the position of the subregion, it is automatically ensured that the observed subregion is relevant, in particular is in a direct surrounding area of the tracing point, so that in particular points which follow the current tracing point in the manufacturing process, in particular directly follow the current tracing point, already lie in the observed subregion. It is therefore possible to react dynamically and very quickly to corresponding disturbances or imperfections, in particular almost in real time.

Moreover, imaging quality close to the center of the array of the detector can be the highest. This is correspondingly utilized in the case of such configurations.

According to at least one embodiment, the device includes a filter, in particular a dichroic filter, which is arranged at the beam splitter and/or between the beam splitter and the detector.

As a result, a retroactive effect of the fusing beam on the detector image can be minimized or ruled out.

Instead of or in addition to the dichroic filter, narrowband notch filters, in particular adapted to a laser wavelength of the fusing beam, may be used.

If the fusing beam is a polarized laser beam, a polarizing filter may also be used as the beam splitter.

According to at least one embodiment, the device includes the heat source, that is to say in particular the laser source or the electron beam source.

According to at least one embodiment, the scanning unit includes one or more deflecting mirrors, which, by means of the control unit, serve for directing and deflecting the fusing beam and in corresponding embodiments likewise the imaging beam, and consequently for changing the position of the subregion.

According to at least one embodiment, the imaging unit has one or more actuators, which are designed to readjust the detector and/or a lens system of the imaging unit, in particular by being activated by the control unit, in a way corresponding to a deflection of the fusing beam by the scanning unit for the imaging of the subregion.

A movement of the fusing beam during the imaging of the subregion onto the detector may have the effect, because of the beam deflection, for example of causing blurring of the image content or instances of unsharpness of the movement, also referred to as “motion blurring”. This can be at least partially compensated by the readjusting of the detector or the lens system.

According to at least one embodiment, the device, in particular the control unit, is designed to couple the imaging of the subregion temporally with a deflection of the fusing beam by the scanning unit in such a way that a movement of the fusing beam during the imaging of the subregion is prevented or avoided.

This represents an alternative or additional possibility for the avoidance of instances of unsharpness of the movement.

According to at least one embodiment, the device has a light-field camera or a plenoptic camera or a multiple-aperture camera, which includes the detector.

In various embodiments of the device, the light-field camera may include a main lens and an array of micro-lenses, which is arranged between the main lens and the detector.

The array of micro-lenses may divide a corresponding imaging beam path into subapertures. For each of these subapertures, a separate image with a slightly different viewing angle is then produced for example on the detector as a result of the spatial offset of the micro-lenses. The spatial structure of the subregion can then be calculated from the slightly different subimages by means of methods of triangulation, and two-and-a-half-dimensional or three-dimensional images are produced.

According to at least one configuration, different micro-lenses of the array of micro-lenses have different focal lengths. In particular, two or three lens types with different focal lengths may be used for the micro-lenses. This allows a depth measurement to be further improved.

As a difference from conventional triangulation or light-section methods, such as structured-light projection or laser triangulation, a light-field camera offers the advantage that there is no asymmetrical preshaping of the edges, for example as a result of a prescribed direction of triangulation due to the structure of the hardware.

According to at least one embodiment, the light-field camera has a lens system with the main lens, the lens system having a focusing device.

According to various embodiments, the focusing device is configured as an autofocusing device.

According to various embodiments, the lens system of the light-field camera is configured as a zoom lens system, for example in order to be able to set the magnification or resolution in the subregion of the light-field camera.

The use of the light-field camera, in particular in embodiments with micro-lenses of different focal lengths, allows a greater depth of field range to be achieved. This makes it possible to partially or fully compensate for an unsharpness which changes for example along a direction of a plane of incidence of the imaging beam.

According to at least one embodiment, the evaluating unit is designed to determine at least one item of topographical information of the subregion on the basis of the at least one detector signal.

The topographical information may in this case be determined in particular from an item of depth information or two-and-a-half-dimensional or three-dimensional information recorded by means of the light-field camera.

According to at least one embodiment, the evaluating unit is designed to determine a deflecting position, in particular an actual current deflecting position, of the fusing beam on the basis of the at least one detector signal.

According to at least one embodiment, the device has a focusing unit, which includes in particular an f-theta lens. The focusing unit is arranged between the scanning unit and the tracing surface or the powder bed and serves for focusing the fusing beam onto the tracing point.

Since, due to the scanning and deflection by means of the scanning unit, the fusing beam passes through the focusing unit, in particular an f-theta lens, with different beam inclinations at different points, geometrical aberrations which in particular cannot be compensated, or not fully, by lens design can occur.

Therefore, embodiments of the device by means of which an actual deflecting position of the fusing beam can be determined are particularly advantageous. This allows the aberrations to be at least partially compensated.

Generally, the fusing beam is not necessarily perpendicular to a plane of the tracing surface. Use of the light-field camera allows a two-and-a-half-dimensional or three-dimensional record of the subregion to be obtained, which in turn allows conclusions to be drawn concerning the deflecting of the fusing beam, in particular by evaluating a distortion of the subregion or of the image of the subregion in comparison with a perpendicular beam without deflection.

In various embodiments, the device has a spectroscope and/or a spectrometer, which is designed and arranged to record light emanating from the tracing surface and generate on the basis thereof a spectrometer signal which includes items of spectrometric or spectroscopic information about the light.

According to various embodiments, the device may include one or more sound sensors, particular structure-borne sound sensors or microphones. The sound sensor is in this case coupled with the workpiece, that is to say is for example arranged directly on the workpiece or is arranged on a support on which the powder bed or the workpiece is located.

By means of a sound sensor, for example sound signals that contain items of information about cracks, spatter and the like occurring in the workpiece during manufacture can be generated.

According to various embodiments, the device may also include further sensors, for example sensors for measuring a mechanical stress in the workpiece.

According to at least one embodiment, the device has an illuminating device, which is designed to at least partially illuminate the subregion.

The illuminating device may be designed to illuminate the entire tracing surface or the entire powder bed. The illuminating device may as an alternative or in addition be designed to illuminate an illuminating region, which includes or partially includes the subregion, in a dynamically variable manner, for example coupled with a movement or changing of the subregion.

According to at least one embodiment, the illuminating device, in particular activated by the control unit, is designed to change the illuminating region, in particular to change it dependent on a position or the changing of the subregion.

The term “illumination” may be understood for example as illumination with light, in particular visible light. A wavelength or a wavelength range of the illumination light or of the light for the illumination is for example made to match a sensitivity or a sensitivity spectrum of the detector.

The illumination allows the light available for the imaging of the subregion on the detector, and consequently an image quality of the imaging, to be improved.

According to at least one embodiment, the illuminating device may switch the illumination on and off.

In particular, the illuminating device and/or the control unit may be designed in such a way that the illumination is switched off during a thermographic imaging or thermographic examination or recording of the subregion.

In this way it can be ensured that the thermographic recording is not falsified by the light of the illuminating device.

According to at least one embodiment, the light for the illumination, that is to say the illuminating light and/or an illuminating beam, may be coupled into the beam path of the fusing beam. This allows the position of the illuminating region to be coupled to the subregion, so that changing of the position of the illuminating region can take place synchronously with changing of the position of the subregion.

According to at least one embodiment, the device includes an optical system for beam shaping, which is arranged between the illuminating device and the scanning unit or between the illuminating device and the tracing surface or the powder bed.

According to at least one embodiment, a light source of the illuminating device is arranged and designed in such a way that it can couple light for the illumination on an input side of the scanning unit into a beam path of the fusing beam.

The light source may for example include one or more laser sources and/or one or more light-emitting diodes.

The light sources may for example couple directly into the beam path of the fusing beam, that is to say be arranged in a direct surrounding area of the beam path or at an edge of the beam path.

As an alternative or in addition, the device may include a further beam splitter, which is arranged between the detector and the beam splitter for coupling out the imaging light or imaging beam. The further beam splitter is arranged in particular in such a way that the light source of the illuminating device can couple the illuminating light or the illuminating beam into the beam path of the fusing beam via the further beam splitter and the beam splitter.

According to at least one embodiment, at least one further light source of the illuminating device is arranged between the scanning unit and the tracing surface or the powder bed.

The further light source may be arranged in particular between the f-theta lens and the tracing surface or the powder bed and/or around the f-theta lens or the focusing unit.

The at least one further light source may for example be arranged inside a working space, in particular outside a working space of the device that is closed off or can be closed of, within which the tracing surface and the workpiece are located. In particular, the at least one further light source may be arranged between the scanning unit and a covering or a covering window of the working space.

According to such embodiments, the entire working space or a large part or a great part of the working space can be illuminated.

An arrangement outside the working space can protect the further light source from dirt and the like.

According to at least one embodiment, the detector is designed to generate at least one detector signal on the basis of the image of the subregion. The device has an evaluating unit for the evaluation and/or processing of the at least one detector signal.

The evaluation and/or processing of the detector signal may for example include a representation of the image of the subregion, for example on a display device.

The evaluation and/or processing may also include storing of the detector signal or of items of information or data determined on the basis of the detector signal.

The evaluation and/or processing of the detector signal may also include an evaluation of image data of the image, in particular for the detection of flaws or for the thermographic assessment or rating.

According to at least one embodiment, the evaluating unit is designed to ascertain at least one thermal characteristic, in particular for the thermographic recording or evaluation, of the subregion on the basis of the at least one detector signal.

The at least one thermal characteristic may for example include a temperature of the tracing surface or of the powder bed in the subregion or a temperature distribution or a temperature profile of the temperature in the subregion.

The at least one thermal characteristic may as an alternative or in addition include a cooling behavior or a cooling parameter or a cooling time in the subregion. The thermal characteristic may also include a temperature or temperature distribution at the tracing point or around the tracing point.

The ascertaining of the thermal characteristic on the basis of the at least one detector signal takes place for example on the basis of one of the detector signals or a number of the at least one detector signals.

Energy introduced into the powder bed or the workpiece by the fusing beam, in particular energy introduced into the subregion, may lead to an increase in the temperature of the powder bed or of the workpiece or of the tracing surface in the subregion. Correspondingly, the subregion may radiate energy in the form of thermal radiation and/or in the form of visible light. In particular, the subregion may radiate electromagnetic radiation in the visible and/or infrared range, in particular in the near-infrared range. An intensity of the radiated electromagnetic radiation allows conclusions to be drawn concerning the temperature or temperature distribution or the at least one thermal characteristic.

In particular, the subregion may appear as a Lambert radiator or black body or almost as a Lambert radiator or a black body.

A value of the temperature of the subregion may for example be proportional to a maximum wavelength of a spectrum of the electromagnetic radiation thermally emitted by the subregion. In particular, Wien's displacement law may apply, or approximately apply.

Such thermographic monitoring and observation of the subregion allows a melting behavior of the material to be observed and monitored. In a corresponding way, temperature control can be performed, for example by means of energy control of the fusing beam, in order to control the temperature of the subregion in real time to a desired temperature, for example to a constant target temperature. Accordingly, more homogeneous material properties can be achieved, and in particular flaws due to locally excessive temperature or too low a temperature, which may for example lead to inadequate melting of the material, can be avoided.

According to at least one embodiment, the detector has a silicon-based sensor, which has a sensitivity at least in the visible range of the near-infrared range, for example in a range of 300 nm to 1100 nm.

Sensitivity may be understood here as meaning for example a sufficiently high sensitivity to allow imaging of a quality sufficient for the respective purposes.

According to at least one embodiment, the detector has a sensor based on a compound semiconductor, for example indium gallium antimonide or zinc selenide. Such sensors are for example particularly sensitive in the infrared range.

According to various embodiments, the camera may be formed as a thermoelectric camera for a near-infrared and/or a far-infrared range.

According to at least one embodiment, the camera includes a polarization filter and/or the detector is formed as a polarization-sensitive detector.

In such embodiments, the evaluating unit may for example be designed to ascertain an item of material information of the material of the powder bed or of the workpiece on the basis of the at least one detector signal, in particular on the basis of an item of polarization information derived or determined from the at least one detector signal. The evaluating unit is for example designed to ascertain the at least one thermal characteristic on the basis of or in dependence on the material information.

Different materials or material classes can have different effects on the polarization of the light reflected by the material. Correspondingly, materials may differ on the basis of the polarization information or the material information.

Accordingly, the evaluating unit may for example be designed to provide different material-dependent thermal calibrations and to apply a corresponding thermal calibration in the determination and ascertainment of the thermal characteristic.

According to a further independent aspect of the improved concept, a device for the additive manufacture of a workpiece is provided. The device has a scanning unit, which is designed to direct a fusing beam onto a tracing point on a tracing surface. The device also has a control unit, an imaging unit and a light-field camera with a spatially resolving optical detector. The imaging unit is designed and arranged to image the tracing surface or the powder bed or a subregion of the tracing surface on the detector.

Such embodiments have in particular the advantages of the light-field camera set out above.

According to a further independent aspect of the improved concept, a method for monitoring the additive manufacture of a workpiece is provided, wherein, for the manufacture, a fusing beam is directed onto a tracing point on a tracing surface. The method includes recording an at least two-dimensional spatially resolved image of a subregion of the tracing surface, wherein a position of the subregion is changed during the manufacture. At least one detector signal is generated on the basis of the image. The manufacture of the workpiece is monitored on the basis of the at least one detector signal.

The monitoring may for example include observing, evaluating and/or processing of the image and/or of the detector signals.

According to a further independent aspect of the improved concept, a method for process control of the additive manufacture of a workpiece is provided. For this purpose, the manufacture of the workpiece is monitored according to a method based on the improved concept for monitoring the additive manufacture. At least one thermal characteristic of the subregion is ascertained on the basis of the at least one detector signal. At least one process parameter for the manufacture is fixed or changed dependent on the at least one thermal characteristic.

The fixing or changing of the at least one process parameter may for example include the calculating of optimized or updated tracing data for controlling the scanning device.

The fixing or changing of at least one process parameter may also include the generating and/or outputting of an item of information, in particular an item of status information, with respect to potential faults or deviations from a target parameter during the manufacture.

The fixing or changing of the at least one process parameter may for example also include an abnormal termination of the tracing process, in particular if it is found that a tolerance is exceeded, there is contamination or cracks or other faults are identified.

The fixing or changing of the at least one process parameter may also include the fixing or changing of a coating parameter, for example a layer thickness for the coating of the workpiece, the fixing or changing of a fusing beam parameter, for example a deflecting speed, or energy of the fusing beam.

The fixing or changing of at least one process parameter may also include the fixing or changing of a focusing parameter, for example of the focusing unit, in particular the f-theta lens.

According to a method for process control according to the improved concept, therefore an online or real-time process management, in particular thermal process management, is made possible. Correspondingly, the influence of faults, which may for example lead to the usability of the workpiece being restricted or to a risk of failure of the workpiece in later operation, or further problems during the additive manufacture which may occur as a result of thermal inhomogeneities, can be avoided. This therefore allows a thermally particularly stable process to be created and to be reproducibly performed.

According to at least one embodiment, a sound signal is recorded by a sound sensor coupled with the workpiece and the fixing or changing of the at least one process parameter is carried out dependent on the sound signal.

The sound signal can be used for example to determine an item of information concerning possible crack formation in the workpiece or concerning material spatter during manufacture.

According to at least one embodiment, the sound signal is filtered, in particular high-pass-filtered, and the at least one process parameter is fixed or changed dependent on the filtered sound signal.

The high-pass filtering allows a detected frequency range to be limited in the downward direction, for example in order to largely suppress acoustic disturbances from the surrounding area of the device or from drives.

As an alternative or in addition to the filtering of the sound signal, a microphone which is designed and adapted for high frequency ranges may be used as the sound sensor.

The microphone may for example be formed as a piezo microphone, as an optical microphone or as a microphone with a moving coil.

The microphone may also be formed as a micro-electromechanical system MEMS, in particular as an optical MEMS.

According to at least one embodiment, a spectrometer signal is generated on the basis of light emanating from the powder bed or the subregion or the tracing surface or the workpiece and the fixing or changing of the at least one process parameter is carried out dependent on the spectrometer signal.

According to a further independent aspect of the improved concept, a computer program is provided, with commands which, during execution of the computer program by a computer system, cause a device according to the improved concept to carry out a method for monitoring additive manufacture or a method for process control of the additive manufacture according to the improved concept.

The computer system may in particular be comprised by the device. The computer system may for example include the control unit, the evaluating unit and/or a further processor unit for carrying out required computing steps.

According to a further independent aspect of the improved concept, a computer-readable storage medium is provided, on which a computer program according to the improved concept is stored.

Further embodiments of the method for monitoring the additive manufacture according to the improved concept arise directly from the various embodiments and implementations of a device based on the improved concept and vice versa.

Further embodiments of the method for process control according to the improved concept arise directly from the various embodiments and implementations of the device based on the improved concept and vice versa.

In particular, a device according to the improved concept may be formed, in particular programmed, for carrying out a method according to the improved concept.

The invention is explained in more detail below on the basis of specific embodiments and associated schematic drawings. In the figures, elements that are the same function or functionally the same are provided with the same reference signs. It may be that the description of elements that are the same or functionally the same is not necessarily repeated in different figures.

In the figures:

FIG. 1 shows an embodiment given by way of example of a device according to the improved concept;

FIG. 2 shows a further embodiment given by way of example of a device according to the improved concept;

FIG. 3 shows a further embodiment given by way of example of a device according to the improved concept;

FIG. 4 shows a further embodiment given by way of example of a device according to the improved concept;

FIG. 5 shows a further embodiment given by way of example of a device according to the improved concept;

FIG. 6 shows a further embodiment given by way of example of a device according to the improved concept;

FIG. 7 shows a flow diagram of an embodiment given by way of example of a method for process control according to the improved concept;

FIG. 8 shows a flow diagram of a further embodiment given by way of example of a method for process control according to the improved concept; and

FIG. 9 shows a flow diagram of a further embodiment given by way of example of a method for process control according to the improved concept.

All of the embodiments of the device and the methods described with respect to the figures can be applied to methods for manufacturing from a powder bed. By analogy, all of the configurations can be applied to methods without a powder bed. A tracing surface then correspondingly takes the place of the powder bed.

In FIG. 1, an embodiment given by way of example of a device according to the improved concept is schematically shown.

The device serves for the additive manufacture of a workpiece, for example from a powder bed 1. The powder bed 1 may be arranged in a working space, which is for example entirely or partially enclosed by a housing (not shown).

A heat source 14 is designed to generate a fusing beam 3, in particular a laser beam or an electron beam.

The device includes a scanning unit 2, also known as a scan unit, which can receive the fusing beam 3 on an input side, which is facing the heat source 14. An optical system 15 for beam shaping of the fusing beam 3 may be optionally arranged between the scanning unit 2 and the heat source 14.

The device also includes a focusing unit 16, which is formed for example as an f-theta lens or contains such a lens, and which is arranged on the output side with respect to the scanning unit 2, that is to say in particular between the scanning unit 2 and the powder bed 1. By means of the focusing unit 16, the fusing beam 3 can be focused and directed onto a tracing point 4 on a surface of the powder bed 1 or of the workpiece. For manufacturing the workpiece, the scanning unit 2 can be activated, for example by a control unit 6 of the device, in order to deflect the fusing beam 3 as required for manufacturing the workpiece according to an order.

The device also has an imaging unit 7, by means of which a subregion 8 of the powder bed 1, in the example shown of FIG. 1 a subregion 8 around the tracing point 4, can be imaged onto a detector 5 of the device.

The detector 5 is designed as a spatially resolved detector with an array of light-sensitive sensors and may for example be part of a camera. The imaging unit may for example include a beam splitter 9, which is arranged between the heat source 14 and the imaging unit 2. The beam splitter 9 allows light that impinges on the beam splitter 9 from the subregion 8 via the imaging unit 2 to be coupled out and directed onto the detector 5.

Optionally, the imaging unit 7 includes a lens system 10 for beam shaping and/or focusing the coupled-out light on the detector 5.

Also optionally, the imaging unit may have a filter 17, which preferably allows light to which the detector 5 is sensitive to pass and preferably blocks or attenuates light which corresponds to a wavelength or a wavelength range of the fusing beam 3.

Optionally, the device may also have an illuminating unit 11, in particular with a light source 13 and an optional beam-shaping optical system 18. The illuminating unit 11 is arranged and designed in such a way that it can couple an illuminating light 12 into the beam path of the fusing beam 3 and thereby illuminate an illuminating region on the powder bed 1, which at least partially includes the subregion 8.

In the example shown of FIG. 1, the imaging unit 7 or the illuminating unit 11 has for this purpose a further beam splitter 26, which can couple the illuminating light 12 initially into a beam path of the light for the imaging of the subregion 8 onto the detector 5 and then for example via the beam splitter 9 into the beam path of the fusing beam 3.

In the example shown, therefore both the subregion and the illuminating region are coupled directly to the fusing beam 3 in such a way that, when there is a deflection of the fusing beam 3, the scanning unit 2 synchronously also deflects the illuminating light 12 and the imaging light for the imaging of the subregion 8 onto the detector 5.

In FIG. 2, a schematic representation of a further embodiment given by way of example of the device is shown.

The embodiment of FIG. 2 differs from that in FIG. 1 in that the illuminating device 11 has further light sources 19, 19′, which can couple the illuminating light 12 directly into the beam path of the fusing beam 3. For this purpose, the light sources 19, 19′ are for example arranged around the beam path of the fusing beam 3, for example at the beam splitter 9.

In such embodiments, it is possible to dispense with the further beam splitter 26.

In FIG. 3, a schematic representation of a further embodiment given by way of example of the device is shown.

The embodiment of FIG. 3 differs from that of FIG. 2 in particular in that the further light sources 19, 19′ are arranged between the scanning unit 2 and the powder bed 1, in particular outside a working space housing 27, within which the powder bed 1 is arranged. The further light sources 19, 19′ may for example direct the illuminating light 12 through a covering window 28 of the working space housing 27 directly onto the powder bed 1. An illuminating region 24 can consequently cover large parts or the entire powder bed 1 and the workpiece.

As is directly evidence to a person skilled in the art, individual features, in particular the various exemplary embodiments of the illuminating unit 11 as shown in the figures of FIG. 1 to FIG. 3, can be combined in any desired way.

The devices as they are shown in FIG. 1 to FIG. 3, or else in FIG. 4 to FIG. 6, can be used in particular for monitoring additive manufacture and/or for process control of additive manufacture according to respective methods based on the improved concept.

In particular, process monitoring and process control can be carried out in real time, or almost in real time, in particular online, by the device based on the improved concept.

According to a device as shown in FIG. 1 to FIG. 6, the imaging unit 11, which includes in particular an imaging optical system, is used to image the subregion 8, in particular the subregion 8 around the tracing point 4 onto the spatially resolved detector 5. In a way corresponding to a resolving power of the optical system used, which is dictated in particular by an available numerical aperture, a pixel size chosen to be at least half as great as a resolution limit determined on the basis of a Rayleigh or Sparrow criterion can be achieved. During scanning with a resolution of for example 10 μm, in the case of a sensor size of the detector of 10 megapixels and an average edge length of approximately 3000 pixels, a recording region of an edge length of over 30 mm, that is to say a surface area of around 10 cm², is obtained. In the case of methods for additive manufacture from a powder bed, a grain size of a powder for the manufacturing, in particular a metal powder, lies for example in a range of about 10 μm. Other parameterizations are for example possible to obtain optimum imaging conditions in other specific applications.

As shown in FIG. 1 to FIG. 6, the light for the imaging on the detector may be branched off from the beam path of the fusing beam 3 by the beam splitter 9. Due to the arrangement of the beam splitter 9 between the heat source 14 and the scanning unit 2, the optical system always remains centered in relation to the fusing beam 3, in particular independently of a deflecting state of a deflecting mirror of the scanning unit 2 in the respective tracing process. The location of the fusing beam 3 may be advantageously arranged in a central region of the detector image, since it is here that the tracing process then takes place and, for example in the case of SLM, forms a melting region (“melt pool”).

The optional illuminating system allows particularly high-grade images to be recorded. An illuminating wavelength may in this case be adapted to a sensitivity range of the detector 5.

The illuminating unit is advantageously formed such that it can be switched on and off, so that, on the one hand, in the switched-on state, for example the entire field of view can be illuminated with a basic illumination. Since a tracing region and regions surrounding this tracing region in the powder bed 1 or on the workpiece can also radiate in the infrared range or in the visible spectral range as a result of a correspondingly increased temperature, these regions may appear even brighter in the image. On the other hand, in the switched-off state of the illuminating unit 11, apart from possible ambient light, then only the self-lighting of the tracing region and its surrounding area can be seen. This region can then for example be thermographically recorded and assessed in its temperature.

The subregion 8 therefore lights up as a result of the energy introduced by the fusing beam 3, because the heated material partly thermally radiates the energy again. Consequently, the brightness with which an object appears in the image in the detector 5 correlates with the temperature of this object, for example the subregion 8. This assignment of brightness to recording parameters, such as exposure time or magnification, or to settings of an imaging optical system, such as for example aperture or stop, or material parameters, such as material, grain size, emissivity of the powder or of correspondingly fused material, can be recorded with a thermometric calibration and then used for measuring, in particular thermometric measuring.

With the thermometric measuring, it is possible in particular to convert a brightness distribution in the image directly into a temperature distribution of the workpiece, so that a thermal profile of the workpiece can be detected and measured with a device according to the improved concept in a region around the fusing beam 3, in particular in the subregion 8.

If the emissivity of the powder differs from that of the sintered or melted material, it may be advantageous and expedient first to analyze the image by image processing before applying the thermometric calibration, in order to determine which image regions are covered with powder and which are covered with sintered or melted material. After that, for example the respective thermal calibration can take place with respect to the types of material present.

As a result of the processing, it is possible for example in the case of SLM methods for sintered material to occur at the edge of a tracing path, for example if the energy or temperature was not sufficient for complete melting and the material was only incipiently melted, and thus adjacent powder particles were sintered. It may be generally advantageous for meaningful thermometric calibration to distinguish between a number of types of material in a way corresponding to the material configurations that are distinguishable in the camera image, that is to say in the image on the detector 5, and then to provide specific individual thermal calibrations for these. If types of material are not directly distinguishable in this way, it may also be advantageous to make the material assignment for example on the basis of a lateral distance from the tracing path, because it may possibly be known a priori, for example from laboratory or tracing trials, how different material composites are obtained at a distance from the tracing path.

For optically distinguishing the material, it may be advantageous to illuminate a viewing region of the detector 5 with unpolarized, polarized or partially polarized light of a known polarization state and to record the image with a polarization-sensitive camera. A polarization-sensitive camera may be understood here as meaning a camera which has a polarization-sensitive camera chip of a corresponding structure. Alternatively, a camera in which a polarization filter 17 is arranged before a conventional camera chip may be provided, the polarization filter preferably being on a path of the beam between the beam splitter 9 and the camera chip, that is to say the detector 5, either having been introduced into the beam path or possibly being variable in the direction it can be passed through, so that, with different settings of the polarization filter 17, the polarization state of the light from the object region becomes measurable.

Instead of distinguishing the material behavior on the basis of the changing of the polarization state in the reflected light in comparison with the radiated-in illuminating light 12, a reflection behavior of the subregion 4 can also be used. If one has for example a structured illumination, which for example contains two grid patterns that are for example turned with respect to one another by a fixed angle, for instance 45°, and one of the grid patterns is projected sharply onto a surface of the powder bed 1 of the workpiece while the other pattern is radiated diffusely, a type of material, for example in powder form or melted, can be identified on the basis of the reflection quality by means of deflectrometry or structured-light projection and the respective degree of reflection or the contrast.

The imaging of the subregion 8 on the detector 5 can be performed for example with a camera, which includes the detector 5.

A record of the image taken with the camera is advantageously coupled with the fusing beam 3 or the imaging unit 2, in order as far as possible only to record an image with a light flash, in order that blurring of the image content, or instances of unsharpness of the movement or motion blurring, are not caused by a movement of the fusing beam 3, and consequently also of the observation beam path, as a result of the beam deflection in the imaging unit 2.

In principle, motion blurring can be compensated by means of known motion deblurring methods. For this, a relative movement between the subregion 8 and the camera must be known, so that consequently at least relatively large structures are better identifiable and can be better represented in a contrasted manner.

As an alternative or in addition, the detector 5 and/or the lens system 10 may be equipped with one or more actuators (not shown), so that a readjustment of the lens system 10 and/or of the detector 5 or of the camera can be performed in a way corresponding to a movement of the tracing beam 3. For this purpose, for example, a current position of the imaging unit 2 or of a deflecting mirror of the imaging unit 2 or a position of the tracing point 4 may be known, so that the items of movement information can be determined from a corresponding location signal.

In one embodiment, the detector 5 may for example be formed as a camera sensor, which is movable with respect to the lens system in a direction within a detector plane. Movability perpendicularly to the detector plane may likewise be advantageous, for example to compensate for defocusing due to the scanning system 2 or the f-theta of the focusing unit 16, for example at edges of the field of view. With a readjustment of the detector 5 perpendicularly to the detector plane, the focus can then be readjusted in the best possible manner.

In addition to the movability of the detector 5, the detector may for example be equipped with a cardanic suspension with an effective rotation point in the middle of the detector 5. This may be advantageous because it is then also possible to compensate for an inclination of the subregion 5 in relation to the optical axis over the working region of the device. If, particularly advantageously, the distance of the rotation point from the detector surface is chosen to match a magnification ratio of the focusing unit 16 or a deflection by the scanning unit 2 or magnification by the imaging optical system, complete correction of the displacement, inclination and focus is possible with just three drives for the detector 5.

As an alternative or addition to the movements of the detector 5 mentioned, other compensation elements are also conceivable. Thus, for example, tilting of the image may also be achieved by decentering of at least one lens or group of lenses in the imaging optical system, or special correction elements for the displacement and correction of the possible aberrations, for example astigmatism or spherical aberrations, may be provided for this purpose. These elements may be formed for example with a plate, in particular a plane-parallel plate, which can be tilted about two axes or can be turned for example about an optical axis and can be tilted perpendicularly to the optical axis, in the imaging optical system between the beam splitter 9 and the detector 5. With suitable design of the geometry, the tiltable plate can, at least to the greatest extent, correct both a focal position and the aberrations due to the possible inclined beam path of the fusing beam 3 in relation to the tracing location 4.

In the case of a configuration with turning and tilting, two oppositely arranged wedge plates, which are for example tiltable with respect to one another about an axis parallel to the vertex axis of the wedge plates, may be provided instead of the tiltable plate. It is in this way also possible to achieve a beam deflection of the fusing beam 3 that can be set and can compensate for the inclination of the imaging beam with respect to the subregion 8 or the powder bed 1 and allows the image on the detector 5 to be set sharply over the full surface area.

In the case of additive manufacturing methods such as for example SLM or SLS, great heating of the material takes place, so that thermal radiation of the subregion 8 can already be detected by cameras in the near infrared or visible spectral range. Alternatively, cameras with sensitivities in the infrared range or thermoelectric cameras for near infrared and/or far infrared may also be used.

In order to minimize or rule out a retroactive effect of the fusing beam 3 on the image on the detector 5, the filter 17 may include a dichroic filter or a narrowband notch filter, in particular adapted to a wavelength range of the fusing beam 3, for a wavelength of the fusing beam 3. As an alternative or in addition, a corresponding filter may be arranged in the beam splitter 9. If the fusing beam 3 contains polarized light, the polarization may also be used for efficient filtering.

By means of the device according to FIG. 1 to FIG. 6, detection can also take place, as described, in regions adjacent to the current tracing point 4, in particular from earlier traced paths or else in the powder bed. With the knowledge of the temperature in the workpiece, the current tracing process can then also be adapted in its parameters such that for example a temperature profile that is as uniform as possible is achieved when tracing. Thus, for example, thermal stresses which can occur due to the local heating in the workpiece in the manufacturing process can be minimized.

Devices based on the improved concept according to FIG. 1 to FIG. 6 allow surface-area imaging of the subregion 8 around the tracing point 4. Imperfections such as defects, flaws, excess material, spatter and so forth, in particular directly before the tracing point 4 and also in an overlapping region, can be detected.

Furthermore, a thermal two-dimensional image in which a temperature profile in the subregion 8 becomes measurable can be generated. Correspondingly, adapted control of fusing beam power can be achieved for the most homogeneous possible temperature control at the tracing point 4 and in the subregion 8. A topography of the subregion 8 can also be detected by three-dimensional methods such as structured-light projection or deflectometry.

As an alternative to the embodiments shown in FIG. 1 to FIG. 6, in which the light for imaging the subregion 8 on the detector 5 has been coupled out from the beam path of the fusing beam 3, a camera with the detector 5 may also be directed directly into the working space and, for example with its own kinematics, follow the fusing beam 3 or the tracing point 4. In particular, the fusing beam 3 may in this case be followed by means of a procedure based on image processing. In this case, with corresponding activation, motion blurring can also be avoided.

FIG. 4 schematically shows a further embodiment given by way of example of a device according to the improved concept. The basic structure of the device corresponds to that shown in FIG. 1.

The device according to FIG. 4 includes a light-field camera 20, also referred to as a plenoptic or multiple-aperture camera. The light-field camera 20 includes the detector 5, the lens system 10 and also the optional filter 17.

Furthermore, the light-field camera 20 includes for example an array of micro-lenses 21, which are arranged between the lens system 10 and the detector 5. By means of the micro-lenses 21, a corresponding imaging beam path is divided into subapertures. For each of these subapertures, a separate image is then produced on the detector 5, with slightly different viewing angles each, as a result of the spatial offset of the micro-lenses 21. A spatial structure of the subregion 8 can then be calculated from the slightly different subimages by means of methods of triangulation, and two-and-a-half-dimensional or three-dimensional images are produced. In order to further improve a depth measurement, in different focal length may be used for different lenses of the micro-lenses 21. For this purpose, lenses with two, three or more different focal lengths may be used.

As a difference from conventional triangulation or light-section methods, such as structured-light projection or laser triangulation, an asymmetrical preshaping at edges as a result of the prescribed direction of triangulation and the structure of the hardware can be avoided by means of the light-field camera.

In some embodiments, the light-field camera 20 may monitor the entire powder bed 1 and workpiece in one record. A setting of the light-field camera 20 during manufacture may then advantageously remain fixed or constant.

In other embodiments, the light-field camera 20 may be directed specifically onto regions of the powder bed 1, in particular onto the subregion 8, and these can be inspected with correspondingly high resolution.

In particular, for this purpose the imaging beam for the light-field camera 20 may be guided at least partially coaxially with the fusing beam 3 and impinge on the powder bed 1 coaxially with the fusing beam 3. This is the case in the embodiment given by way of example of FIG. 4.

If pivoting movements are used when changing the position of the subregion 8, an optical axis of the imaging optical system is inclined in a way corresponding to the pivoting movements, and consequently so is the sharply imaged object plane of the optical system, which is for example perpendicular to the optical axis. Consequently, the image sharpness of the imaging changes along the direction of the plane of incidence of the imaging beam. Since, however, the light-field camera 20, in particular in the version with the micro-lenses 21 of different focal lengths, can sharply image a very much greater depth of field range, this unsharpness can be fully or partially compensated.

The imaging onto the detector 5 of the light-field camera 20 can be digitally refocused, which has the consequence that, depending on the present tilting position of the optical axis in relation to a workpiece surface or a surface of the powder bed 1, a sharp image can be calculated for an image plane that is lying obliquely in relation to the optical axis and is conjugate with the tilted object plane via the optical system. As an alternative or in addition, a three-dimensional point cloud of measurement data of the light-field camera 20 may be determined and can then represent the tilted object plane, in particular together with a topography of individual features in the subregion 8, such as for example elevations or depressions, for example material spatter on the powder bed 1 or holes in the powder bed 1. It may also be advantageous for tilting of the data in the three-dimensional point cloud if tilting caused purely by a viewing direction is calculated out of the data set. The data can therefore be represented in a reference coordinate system, preferably a workpiece coordinate system or machine coordinate system.

Compensation of the tilting angle in the image record, for example in one of the ways described, is also advantageous for bringing together measurement data either of the three-dimensional images or of the three-dimensional point cloud comprising the subimages into a coherent image made up of multiple subimages that have been recorded with difference tilting positions.

Images of the light-field camera 20 may be metrically calibrated for example for a fixed setting of the imaging lens system for the focal position and zoom. With metrically calibrated images, stitching can be better performed, because the distortions from the camera image can be minimized.

Instead of measuring different calibrating images, an effect of the optical system for different tilting angles of the beam, and associated effective beam axes, can also be ascertained by simulation and then taken into account for example in an evaluation. Combinations of measurement and simulation are also possible, for example to make use of a time advantage of simulation and on the other hand nevertheless to record a comparison with the specific system as completely as possible.

The light-field camera 20 may be constructed for example as a color camera or black-and-white camera, with a sensitivity range for example in the ultraviolet, visible, infrared, near-infrared, mid-infrared and/or far-infrared spectral range. For an application in SLM or SLS methods, a version with a silicon detector may be advantageous, in particular with a sensitivity range of approximately 400 to 1100 mm.

According to devices as shown in FIG. 4, in particular a direction-dependent three-dimensional or two-and-a-half-dimensional recording of the subregion 8 may take place. The depth of field may for example be increased, in order to be able to digitally compensate for instances of tilting of the imaging beam.

For example, distance control, from a tracing head to the workpiece surface, or to the powder bed 1, may take place almost in real time.

A three-dimensional thermal recording of the component, with or without thermal calibration, is likewise possible. With respect to the thermal recording and calibration, reference is made to the explanations in relation to FIG. 1 to FIG. 3.

In FIG. 5, a schematic representation of a further embodiment given by way of example of a device according to the improved concept is shown. A basic structure of the device corresponds to that of the device according to FIG. 1 to FIG. 4.

The device includes a camera 25, which may for example correspond to the light-field camera 20 and/or may include the detector 5 according to FIG. 1 to FIG. 3. Also shown is an evaluating unit 23, which is coupled with the camera 25. The evaluating unit 23 may for example record detector signals generated by the camera or the detector 5 and on the basis thereof control a manufacturing process for the additive manufacture.

Optionally, the device also includes a spectroscope or spectrometer 22, which can record light emanating from the subregion 8 and on the basis thereof generate spectral signals and supply them for example to the evaluating unit 23.

FIG. 6 shows a further schematic representation of an embodiment given by way of example of a device according to the improved concept. The device of FIG. 6 largely corresponds to the device from FIG. 5.

While in FIG. 5 the beam splitter 9 is provided in order to couple out light from the beam path of the fusing beam 3 and direct it onto the further beam splitter 26, which conducts light on the one hand to the camera 25 and on the other hand to the spectroscope or spectrometer 22, in FIG. 6 the two beam splitters 9 and 26 are arranged one behind the other in the beam path of the fusing beam 3 and independently of one another couple out light for the camera 25 or the spectroscope or spectrometer 22 from the beam path of the fusing beam 3.

A device according to FIG. 5 or FIG. 6 can be used in particular for carrying out a method for process control according to the improved concept, in particular as explained below with respect to FIG. 7 to FIG. 9.

In FIG. 7, a flow diagram for the schematic representation of a method for process control according to the improved concept is shown. In a step 601, detector signals from the detector 4, in particular containing items of two-dimensional, two-and-a-half-dimensional or three-dimensional information about the subregion 8, are recorded and for example transmitted to the evaluating unit 23.

In a step 602, the evaluating unit 23 determines for example a topography of the tracing location 4 or the subregion 8.

The items of information from 601 are possibly used in a step 603 to create a thermal profile of the tracing location 5 or of the subregion 8, for example by means of the evaluating unit 23.

Optionally, in a step 604, spectral signals from the spectroscope or spectrometer 22 may be transmitted to the evaluating unit 23. The spectral signals may for example be taken into account in the ascertainment of the thermal profile.

In an optional step 605, the evaluating unit 23 determines items of information concerning possible instances of contamination in the subregion 8 on the basis of the spectral signals.

In an optional step 606, sound signals or acoustic signals, in particular structure-borne sound signals, from a sound sensor of the device that is coupled with the workpiece are transmitted to the evaluating unit 23.

In an optional step 607, the evaluating unit 23 may determine items of information concerning the occurrence of cracks, stresses or relaxations in the workpiece on the basis of the sound data.

Optionally, in a step 608, further sensors or measuring devices may record further measured variables and pass them on to the evaluating unit 23. In an optional step 609, the evaluating unit 23 may generate for example derived items of process information on the basis of the further measured variables.

The items of information, profiles, topographies and so forth generated in steps 602, 603, 605, 607 or 609 may be used for example in a step 610 for process control, in particular for controlling a tracing process for manufacturing the workpiece by the device. In particular, the evaluating unit 23 may calculate optimized tracing data with a current item of process information on the basis of the items of information and data thus recorded. Deviations of a tracing path or of the tracing point 4 from target values can be minimized or compensated on the basis of the optimized tracing data.

In particular, the evaluating unit 23 may activate the heat source 14 and/or the scanning unit for controlling the tracing process.

Likewise in step 610, the evaluating unit may for example ascertain items of information or items of status information on potential deviations or faults and for example output them to a user of the device, for example via a user interface or a display unit.

In the case of certain serious faults, such as for example when tolerances are exceeded, when there are serious instances of contamination or when cracks occur in the workpiece, in step 610 the evaluating unit 23 may for example also abnormally terminate the tracing process. In particular, for this purpose, the evaluating unit 23 may deactivate the heat source 14.

For calculating the tracing data, in particular the optimized tracing data, for performing further steps described with respect to 610, the evaluating unit 23 may, for example in a step 611, also record target data or layer data for manufacturing the workpiece or for example CAD data and take them into account in the required calculations.

In a step 612, the evaluating unit 23 may activate various system components of the device directly or indirectly in order to control the process; for example, the evaluating unit 23 may activate a coating unit, in order for example to determine or set a layer thickness for the coating after the actual additive manufacture of the workpiece.

In addition or as an alternative, the evaluating unit 23 may for example activate the heat source 14 in such a way that energy of the fusing beam 3 is changed. As an alternative or in addition, the evaluating unit 23 may activate the scanning unit 2, in order correspondingly to compensate for or minimize the deviations. As an alternative or in addition, the evaluating unit 23 may also activate the focusing unit 16, that is to say in particular the f-theta lens, in order to correct a focus.

In FIG. 8, a flow diagram of a further embodiment given by way of example of a method for process control according to the improved concept is shown. In a step 701, a thermal image for example of a melting region or of the tracing location or of the subregion 8 is transmitted to the evaluating unit 23. Optionally, in a step 702, a surface image, in particular a two-dimensional and/or two-and-a-half-dimensional and/or three-dimensional surface image, of the powder bed 1 or of the subregion 8 may be transmitted to the evaluating unit 23.

In step 703, the evaluating unit 23 may for example determine a temperature profile or isotherm on the basis of the thermal image.

On the basis of the surface image, in step 704, the evaluating unit 23 may for example ascertain an item of topography information of the subregion 8 and for example detect holes, spatter, other structures or powder remains.

In step 705, the evaluating unit 23 may for example determine an amount of energy of the fusing beam 3 that is required or is to be adapted, for example from the temperature profile or from the surface image of the subregion 8. As an alternative or in addition, the evaluating and 23 may also determine an operating mode of the heat source 14, for example for optimizing a temperature profile before a tracing operation or, location-dependently, in alternation with the tracing operation.

In a step 706, the evaluating unit 23 may for example activate the heat source 14 and/or the scanning unit 2 and/or the focusing unit 16, for example for adapting the manufacturing process. In particular, in the step 706, the evaluating unit may switch over between different operating modes of the device, for example between a heating mode and a tracing mode.

The step 705 may also for example optionally be assisted here by CAD data or layer data or target data from a step 704.

In FIG. 9, a flow diagram of a further embodiment given by way of example of a method for process control according to the improved concept is shown. A step 801 corresponds to a step 701 in FIG. 8. A step 802 corresponds to a step 702 in FIG. 8. In a step 803, for example, further data such as sensor data, further measured variables, sound signals and/or spectral signals may be transmitted to the evaluating unit 23. A step 804 corresponds to a step 704 in FIG. 8.

In a step 805, the evaluating unit 23 may carry out steps, in particular calculation steps, for thermal process management. In particular, the evaluating unit 23 may determine a dynamic determination of one or more process parameters. The evaluating unit 23 may for example activate one of a number of operating modes of the device, for example a tracing mode, a tracing-and-heating mode or a heating mode.

In a step 806, the manufacture of the workpiece may then be carried out. In a step 807, quality testing of the workpiece may take place. In a step 808, for example, deviations of actual values of the workpiece from target values may be determined and/or defects of the workpiece determined.

In an optional step 809, for example, data from measurements accompanying the manufacture may be provided. In an optional step 810, manufacturing parameters may be provided.

In a step 811, the evaluating unit may example carry out optimization of the model for a dynamic determination of process parameters on the basis of the deviations or defects determined in step 808 and optionally from the data from 809 and the parameters from 810. In particular, structural elements and/or morphologies may be determined. The adaptation of the model may take place in particular component-specifically or region-specific.

In a feedback step 812, the optimized adapted model may for example be taken into account in the thermal process management for the future manufacture of a further workpiece.

In a method for process control according to the improved concept, it may be provided that the signals of further, previously unmentioned sensors or else control or positioning signals or items of information enter processing of the respective measurement data for the purposes of process control.

Process control according to the improved concept uses these items of information concerning the tracing process or the workpiece itself in order to control the tracing process in such a way that the decisive tolerances of the workpiece are minimized and moreover for example also a thermal load and/or temperature gradients in the component are minimized or kept as stable and controlled as possible. As a result, stresses in the workpiece can advantageously be minimized.

Measurements with further sensors also serve for example for even more complete recording of the tracing process with respect to further parameters and variables influencing the quality of the workpiece. For example, the sound measurement is described here.

The process control based on the improved concept allows more precise use of the present items of information to improve the manufacturing result. Process control may for example adopt items of geometrical information from the imagings of the subregion 8, in order for example to monitor and control a focal position or a height positioning in the process. The height control may be used for also indirectly influencing for example a depth effect of the tracing process. Thus, for example, more complex structures, such as overhangs or undercuts, which can occur in typical workpieces, can be manufactured with higher precision.

The layer thickness of the next layer can be set in such a way that for example flaws of the current layer can be reliably filled or protruding parts do not conflict with or have a disturbing effect on the coating process. Typically, such disturbances can build up over a number of layers before there are disturbances in the process. Such disturbances can thus be intercepted by an early correction or countermeasure in such a way as to avoid disturbances of the process.

Heating power or an energy input or laser power, in particular of the fusing beam 3, can be controlled in such a way that the tracing point 4 has a desired lateral extent. For example, working can be carried out in a controlled manner in the workpiece and within a layer with tracing points 4 of different sizes in such a way as to optimize the manufacturing result.

Geometrical guidance of the fusing beam 3 may for example be monitored in such a way that geometrical distortions in the manufacturing process can be corrected online. Possibilities for geometrical fusing beam guidance on the basis of two-dimensional or three-dimensional recording of the subregion 8 are described.

Furthermore, a position and size of structures or adjacent tracing paths may also be determined and taken into account for process control.

The process control also reverts for example to the items of thermal or spectrographic information and signals, for example in order to achieve the most homogeneous or stable temperature possible in the tracing region, to minimize thermal gradients and/or to create a depth profile for the local introduction and dissipation of heat. Furthermore, material changes can be detected, for example oxidation from earlier overheating. Finally, foreign materials can also be detected.

Further items of sensor information, for example sound signals, may for example be taken into account in order to detect crack formations or to detect spatter and/or to determine further manufacture-relevant or process-relevant parameters.

The process control uses the items of information mentioned and possibly further items of information from machines and/or material-specific specifications or else items of geometry information, for example from CAD data, in order to allow optimized process management by deterministic and/or learned assessments and/or modelings.

According to the proposed process control, collected items of information from the manufacturing sequence for the entire workpiece or else for subregions of the workpiece can be analyzed in a detailed manner, for example in order to further optimize the process management, for instance for further similar parts or else for modular or recurring structural elements in the case of comparable workpieces.

An analysis, for example concerning crack formation or material changing or other quality criteria or instances of material contamination, may be used in addition to the analysis of purely geometrical deviations in order to stop or abnormally terminate a manufacturing order that is in progress as soon as for example it is likely or evident that the manufactured workpiece can no longer satisfy existing quality criteria.

If the tracing process has been stopped, a single- or multi-stage heating-up process may also be performed according to the process control, wherein, by means of the fusing beam 3, for example only the workpiece is successively heated up with increasing power until a temperature distribution favorable for a stable tracing process and a corresponding cooling behavior have been achieved.

This method can preferably also be used when hybrid manufacturing methods are used, for example when a further part is to be built onto an existing part or a semifinished product or fabricated in a stable material composite by the additive manufacturing method. Such scenarios may occur in the case of repair and maintenance, where regions have become damaged by wear or removed in the repair process and are to be made good.

Similarly, simple semifinished products involving classical manufacturing methods, such as casting, forging, turning, milling, pressing in various specific configurations, can typically be combined with a serial additive method.

With process control according to the improved concept, in particular by means of the controlled preheating, in particular more filigree and more individual subregions can be added onto a prefabricated semifinished product. 

1. A device for additive manufacture of a workpiece, the device comprising: a scanning unit configured to direct a fusing beam onto a tracing point on a tracing surface; a light-field camera that has a spatially resolving optical detector; an imaging unit configured and arranged to image a subregion of the tracing surface at least two-dimensionally using the spatially resolving optical detector, the spatially resolving optical detector being configured to generate at least one detector signal based on the image of the subregion; a control unit configured to activate the device to change a position of the subregion during manufacture; and an evaluating unit configured to evaluate, process, or evaluate and process the at least one detector signal.
 2. The device of claim 1, wherein the imaging unit includes a beam splitter that is arranged on an input side of the scanning unit in a beam path of the fusing beam.
 3. The device of claim 1, wherein the imaging unit includes an actuator configured to readjust the spatially resolving optical detector, a lens system of the imaging unit, or the spatially resolving optical detector and the lens system of the imaging unit in a way corresponding to a deflection of the fusing beam by the scanning unit for the imaging of the subregion.
 4. The device of claim 1, further comprising an illuminating device configured to at least partially illuminate the subregion.
 5. The device of claim 4, wherein at least one light source of the illuminating device is arranged and configured to couple light for the illumination on an input side of the scanning unit into a beam path of the fusing beam.
 6. The device of claim 5, wherein at least one further light source of the illuminating device is arranged between the scanning unit and the tracing surface.
 7. (canceled)
 8. The device of claim 1, wherein the evaluating unit is configured to ascertain at least one thermal characteristic of the subregion based on the at least one detector signal.
 9. (canceled)
 10. The device of claim 1, wherein the evaluating unit is configured to determine an item of topographical information of the subregion based on the at least one detector signal.
 11. The device of claim 1, wherein the evaluating unit is configured to determine a deflecting position of the fusing beam based on the at least one detector signal.
 12. The device of claim 1, further comprising: a spectroscope, a spectrometer, or a combination thereof that is configured and arranged to record light emanating from the tracing surface and generate on the basis thereof a spectrometer signal that includes items of spectrometric or spectroscopic information about the light; one or more sound sensors that are coupleable with the workpiece; or a combination thereof.
 13. A method for additive manufacture of a workpiece, wherein, for the additive manufacture, a fusing beam is directed onto a tracing point on a tracing surface, the method comprising: recording an at least two-dimensional spatially resolved image of a subregion of the tracing surface using a spatially resolving detector of a light-field camera, wherein a position of the subregion is changed during the manufacture; generating at least one detector signal based on the image using the spatially resolving detector; monitoring the manufacture based on the at least one detector signal; evaluating, processing, or evaluating and processing the at least one detector signal.
 14. The method of claim 13, further comprising: ascertaining at least one thermal characteristic of the subregion based on the at least one detector signal; and fixing or changing at least one process parameter for the manufacture dependent on the at least one thermal characteristic.
 15. The method of claim 14, wherein: a sound signal is recorded by a sound sensor coupled with the workpiece, and the fixing or changing of the at least one process parameter is carried out dependent on the sound signal; a spectrometer signal is generated based on light emanating from the tracing surface, and the fixing or changing of the at least one process parameter is carried out dependent on the spectrometer signal; or a combination thereof.
 16. (canceled) 